Gluing method



' July 21, 1942. H. GALBER 2,290,548

GLUING METHOD 'Filed June 27, 1939 2 Sheets-Sheet 1 0 3 PW W.

Hafiz? Galber,

July 21, 1942. GALBER I 2,290,548-

GLUING METHOD Filed June 27, 1959 2 SheetS -Sheet 2 A L TERA/A TIVEPEEL/M/Nfl/QV COMPEL-15570 26 FLA TEN Pa s:

Jiarzg Qale 7,

Patented July 21, 1942 2,290,548 GLUING METHOD Harry Galber,Seattle,-Wash., assignor to I. F. Laucks, Inc., Seattle, Wash., acorporation of Washington Application June 27, 1939, Serial No. 281,473

2 Claims.

The present invention relates to an improvement in gluing practice.While my new method is particularly valuable in facilitating volumeproduction of hot pressed plywood, it is also applicable in generalgluing practice with fluid or semi-fluid glues by either cold or hotpress methods wherever a glue is spread on at least one of the surfacesto be joined and subsequently solidified while the assembly ismaintained under pressure. For the purposes of this description and theappended claims, these glues may be called dispersed glues and by thatterm I intend to include not only true solutions, but suspensions andadhesive mixtures in general of a spreadable fluid or semi-fluidcharacter.

One of the principal objects of the invention in certain importantapplications is to improve transfer of the adhesive from the spreadsurface to a contacting unspread surface with an improved uniformity ofdistribution and to simultaneously obtain more uniform and bettercontrolled penetration. Another and very important object is to greatlywiden assembly time tolerance. By this term, I mean the permissibleinterval which may elapse between the spreading of the adhesive and theapplication of bonding pressure to the assembled parts. Other objectsare to improve the character of glue bonds, to reduce glue consumption,and to facilitate handling of the spread assemblies.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described, andparticularly pointed out in the claims, the following descriptionsetting forth in detail certain illustrative embodiments of theinvention, these being indicative, however, of but few of the variousways, in which the principle of the invention may be employed.

While, as indicated, the present invention is,-

by no means, confined to the plywood art, one of its most advantageoususes is in that field and consequently the subsequent description willexemplify such use. It will become apparent, however, that the methodmay readily be applied in other ways.

In plywood manufacture, for example, it is the usual practice to spreadthe glue in a fluid or at least semi-fluid condition on both sides ofthe core ply, and, then in making the ordinary three ply panels,assemble the spread core between number of hours, but is reduced to afew minutes in the hot press process. In either case, for best results,it is necessary to obtain a final re-distribution of the spread adhesiveas a thin uniform film over both contacting surfaces. 0btaining aneffective glue transfer from the spread to the unspread surface is avital consideration.

Other features are also essential to obtaining an effective bond withthe least adhesive. In particular, it is necessary to have the gluepenetrate adequately, but not excessively, into the porous wood of bothcontacting surfaces and between them there must be retained a sufficientresidue or fihn to strongly unite the parts. Another considerationnecessary for volume production, is that the gluing conditions allow asufficient time interval to permit successive assembly of a number ofpanels and allow pressing of the group either successively or en masse"without subjecting any units to conditions which would form anon-commercial bond. It may be explained that in the cold process it iscustomary to glue the panels up in rather large batches and then pressthe batches "en masse." This implies that the first panels glued up willnot be subjected to bonding pressure until the batch has been completed,and in practice it frequently requires 15 or 20 minutes to assemble abatch and get it under pressure. The wood plies are either dry or nearlydry and hence very absorbent and consequently during this interval theglue will progressively thicken due to loss of gluewater into the drywood. As the glue consistency increases, its ability both to penetrateand to transfer steadily decreases.

The effect of these tendencies is to make the plywood produced by thiscold process batch method quite variable in quality, the last panelslaid up in each batch often tending to have an inferior starved bond dueto excessive penetration of the adhesive which has not had time tothicken sufliciently before the application of pressure, while the firstpanels in the batch usually suffer to some degree from the reversecondition and show poor transfer with deficient penetration and a weaksuperficial bond due to excessive thickening during the long assemblywtime interval. Generally, the best panels and the only ones exhibitingthe highest order of adhesion are obtained in the middle of the batchwhere intermediate and ideal assembly time conditions have obtained,

The same condition exists to a lesser degree if the hot press process isused. In that case the panels are not ordinarily pressed en masse tweenindividual panels are reduced accordingly.

However, the same differences exist and in hot press practice also, awider assembly time tolerance is much to be desired.

More recently an improved method of hot'press gluing has been developedemploying what is called mastic or semi-fluid glue. This method operateson the principle of initially applying the glue in approximately thethick viscous state which is ideal for best bond formation and thenpressing the plies before any appreciable change from that consistencycan occur. This process is described in the copending application ofTheodore Williams Dike and myself, Serial No. 95,460, now Patent2,178,566. In this process, tolerance of assembly time is still furtherlimited and, unless it is kept very short, the adhesive, having beenapplied in an initially thickened condition, will soon become too thickto either transfer or penetrate properly. I The present invention, whileapplicable to any of the processes described, is particularly beneficialas an improvement on the mastic gluing process because it greatly widensthe restricted tolerance of assembly time and provides the process witha very desirable increase in flexibility.

As an example of the operation of my invention, I will first describethe ordinary procedure of manufacturing fir plywood by the masticprocess and then describe such manufacture by the improved masticprocess which results from applying the principles of the presentinvention. In the manufacture of fir wallboard, for instance, a dry gluebase for a mastic soybean glue is made by mixing 95 lbs. of fine groundsoybean flour with 4 lbs. of fine ground soda ash and 1 lb. of pine oil.100 parts by weight of this dry powder are mixed with 200 parts ofwater. Then parts of hydrated lime separately mixed with 50 parts ofwater are added, followed by 4 parts of caustic soda separatelydissolved in 10 parts of water,

followedby 30 parts of N brand sodium silicate and finally by a mixtureof 1.8 parts carbon bisulfide and 1.2 parts of carbon tetrachloride. Theviscosity one-half hour after making up will then be about 30 MacMichaelwith #18 wire, the ratio of water to dry glue base being 2.6 to 1. Thisis a very heavy bodied semi-fluid glue.

Dry cores at about 3% moisture are spread at the very low rate of 50lbs. of this wet glue per thousand square feet of three-ply panelsemploying rubber covered reticulated or pattern spreading glue rollswith sufllcient pressure on the rolls to cause the core pieces topositively move forward and the semi-fluid glue to be spread at the samespeed and the adhesive to be printed on the wood in a correspondingpattern. In this instance, the glue rolls are grooved spirally witheleven grooves per inch so as to produce an adhesive pattern consistingof a corresponding series of raised adhesive areas or glue ridges withspaces between merely wetted with the adhesive, but free from anyexcess.

The spread cores are laid on backs which have been placed on a conveyorand a face ply is laid on the cores forming the complete assembly whichis then moved into a hot press. Two assemblies are pressed in eachopening. The

press is immediately closed and a pressure of about 200 lbs. per squareinch of panel surface is applied. The assembly time between thespreading of the cores and the application of the pressure may vary fromabout 30 seconds to five minutes. The press plates are heated to auniform temperature of 225 F. and, after seconds, the press is openedand the panels removed.

This method produces extremely well glued plywood with both a very smallconsumption of glue and low injection of glue water into the piles,provided the time of assembly is kept within these narrow limits. It ishighly eflicient because of these features as well as the very shorttime in the press and the panels are more uniform and better glued thanthose produced by the cold process. However, there is still somevariation in the product. For example, upon examination a panel thusmade with an assembly time of only one-half minute was found to showcomplete transfer with entire obliteration of the originalspread-pattern indicating that the glue was redistributed by thepressure into a very uniform film, but there was an excessivepenetration and the panel, while ,fully commercial, showed indicationsof a starved joint with an insufficient residue between the contactingsurfaces to produce a bond of maximum strength. In this case, it wasevident that the panel had been pressed a little too soon afterspreading for ideal results. In this instance, a more ideal panel couldhave been produced with this very short assembly time of one-half minuteby running the glue at a still higher initial viscosity, but thatexpedient would have obiectionably narrowed the tolerance of longerassembly time, causing deficient penetration to become prohibitive afterabout two and a half minutes instead of five minutes. A similar panelmade at the same time with an assembly time of one and one-half minuteswas found to have a very strong and practically ideal bond, whileanother made with the time extended to the permissible maximum of fiveminutes, although fully commercial, was not found to be ideal. Thetransfer was seen to be poor with the original pattern of spread linesstill visible and the .glue penetration into the unspread ply wasinsufficient. Beyond an .assembly time of five minutes the results werefound to fall'oif rapidly.

With other forms of mastic or semi-fluid glue somewhat wider toleranceof assembly time may be attained, particularly by compounding with acertain proportion of more thermoplastic adhesive components. However,thus far a maximum tolerance of twenty minutes has been found to be theapproximate upper limit when using the semi-fluid glues of the masticprocess and even this extension adds considerably to the gluing cost bynecessitating the use of more expensive materials.

It is thus seen that the assembly time tolerance problem is a generalcharacteristic of gluing with dispersed glues regardless of whether coldpress or hot press methods are used. With the cold process a widetolerance is required and there are correspondingly wide variations inthe quality of the panels produced between the permissible extremes.With the ordinary hot process the same condition obtains, but undernarrower limits, and, with the mastic process just described,

the same restriction is also encountered and the changes are more abruptdue to the shorter interval of tolerance.

After observing, for instance, that the mastic panel made with a 30second assembly time had a starved joint with excessive penetration, it

would be logical to expect that any very early pressing of a panel wouldinevitably produce a starved joint. Up to the present, as far as I amaware, this has been the general opinion. I have now discovered that ifthe proper procedure is followed, not only is this untrue, but suchearly application of pressure, instead of being detrimental, may be verybeneficial and produce the unexpected result of greatly widening thetolerance. For instance, in the improved mastic gluing proceduresubsequently described, I am able to extend the tolerance from fiveminutes up to twenty minutes and with a specially compounded mastic gluehaving a normal tolerance of twenty minutes, by my procedure I canextend that period to two hours.

In practicing my invention in the manufacture of fir plywood with masticglue, I may take the assembly and within thirty seconds, instead of hotpressing it, apply a momentary cold pressure nearly up to the crushinglimit of the wood. In this case with Douglas fir the momentary pressureapplied was 250 lbs. per square inch. I then at once released thepressure and subsequently pressed it in the usual manner in the hotpress after an additional interval of ten minutes. The resulting panelwas found to have an ideal bond even better in general quality than thepanel produced with one and one-half minutes assembly time without anypreliminary compression. A duplicate precompressed panel finally pressedafter a total assembly time of twenty minutes, while not showing as gooda bond as the ten minute panel, was entirely commercial and actuallysuperior to that produced after five minutes without precompression.These panels were made with the soybean mastic glue previouslydescribed. I have obtained similar results with mastic panels made witha very high grade glue normally capable of permitting twenty minutesassembly time. By precompressing them excellent panels were producedwith a total assembly time of two hours. A similar beneficial result wasobtained by applying my precompressing method when using the coldprocess. In this case excellent panels were produced after a totalassembly time of forty minutes which were better than panels producedwithout precompression with an assembly time of twenty minutes.

I have found that this improvement is generally applicable to the gluingof porous materials with glues which are spread on at least one surfaceand subsequently solidified under pressure. If both contacting surfacesare spread. similar advantageous results are obtained, the principaldifference being that, since the glue is already present on bothsurfaces, the necessity of obtaining transfer is eliminated. However,the same benefits are obtained in regard to control of penetration andobtaining the proper minutes after spreading and in both cases. ofcourse, it is ordinarily preferable to precompress much sooner. withmastic glues, precompression should not be postponed more than aboutthree minutes after spreading and preferably should take place withinabout one minute.

In regard to pressure, inmost cases, I find that although even lowpressure is beneficial. the best results are obtained when using fairlyheavy pressureyin some cases nearly up to the crushing limit of thewood. High pressures are particularly desirable in treating dense woodshaving small pores or in dealing with originally less fluid glues, suchas mastic even with the soft porous woods. The extent of penetration canbe controlled by varying the pressure in accordance with the consistencyof the glue existing at the time of applying the pressure and thecharacter of the wood or other porous surface to be penetrated. If theglue is very thick or the wood dense and diificult to penetrate, aproportionately higher pressure will be required to obtain a givendegree of penetration and conversely with very fluid glue or very porouswood less pressure will produce the best results. Penetration can alsobe regulated by precompressing early while the glue is still most fluidto induce greater penetrating or by delaying the precompression untilthe glue becomes thicker to avoid too much penetration. Heat may also beused to induce flow and penetration, but is usually unnecessary. Byfollowing these rules, the correct procedure for any given set ofconditions can be found easily.

The principles of my invention can also be applied readily to gluinginsulating board, paper and other porous materials. In the case ofpaper, for the most part, it will be found much more absorbent than woodand, for this reason, comparatively light pressures usually can beemployed and short intervals between spreading, precompression and finalpressing. Some varieties of paper are much less porous than others, sothat the adjustment of the different factors should be modifiedaccording to the conditions.

It has been shown that if the precompressing is applied before the gluehas. substantially changed in its consistency, its effect is toredistribute the adhesive from the area of original deposit in asubstantially uniform penetrating film over both of the contactingsurfaces, thus securing complete transfer from the spread to theunspread surface and simultaneously a desirable immediate and uniformpenetration into both of the contacting surfaces or plies. If theprecompressing pressure is only momentary or of short duration, eventhough the glue has not previously had time to thicken appreciably,nevertheless, starving of thejoint'does not occur as would be the caseif this early pressing was long continued. Instead of that, thedesirable condition of a uniform moderate penetration into both surfacesresults, leaving an adequate residual film between the plies along withthe essential transfer. A further advantage is that these results occurin a short time interval so there is no need for more than a momentaryapplication of pressure. I

I then find that having thus obtained in advance the essential transfer,penetration and adequate residual film of giue'on the surfaces, acomparatively long period can then elapse before the final bondingpressure is applied. Immediately after releasing the precompression, theresidual film which is now much shallower than release of theprecompression, since the adjacent wood has already been saturated, theconsistency changes but slowly and the glue remains at least tacky for along time. Owing to this feature, the final bonding pressure may beapplied either fairly promptly after this initial thickening has takenplace or only after a comparatively long interval and yet very littledifference in the quality of the bond will result. This is, of course,due to the ease with which such tacky surfaces unite with each other.Good commercial bonds result because the transfer and penetrationessentials have already been supplied and all that remains is merely tounite the tacky glue films on both contacting surfaces and hold thesurfaces in good contact during the setting or hardening of the glue. Inordinary gluing without precompression both transfer and penetrationmust for the most part be obtained during the final pressing step, veryoften after the glue has become too much dried up to have the necessaryability to fiow. This difference is characteristic of my process. It isthus seen that in my process the two films on the adjacent ply surfaceswill remain tacky and hence soft enough to unite quite readily, longafter they would be unable to meet the requirements of the old processwhich demands considerable ability to fiow at the time of pressing. Bythe term tacky, therefore, I imply a condition which permits contactingfilms to unite by flow. In the cold process the condition must permit asufiicient amount of flow to be induced by pressure alone, but in thehot process the heat is a valuable aid to inducing fiow since alladhesives of this character are thermoplastic when moist.

When the precompression step is omitted, the final bonding pressure hasto secure simultaneously adequate, but not excessive, penetration intoUooth surfaces, comp ete transfer, and a proper residual film. If thepressing is done early, the transfer requirement is met, but theresidual film is lost and a starved joint results due to the continuingpressure forcing the residual glue deep into the wood. The tendencywhere only one of the contacting surfaces has been spread with glue andthe assembly time is considerable, is towards the other extreme so as tocreate an unfavorable difference between the situation on the twoadjacent surfaces. A deficiency of penetration and transfer results withrespect to the unglucd ply which becomes worse and worse as assemblytime is extended. It is thus seen that in my process the step ofpreliminary pressing avoids both the starved joint and poor transferdifficulties with the additional advantage that not only is assemblytime tolerance greatly extended, but also the resulting bonds are moreuniform and the action of the adhesive becomes more effective. Due tothis, I find there is a saving in glue consumption of about fifteen percent. There is a further advantage also in the handling ofpre-compressed panels when they are finally loaded into the press forfinal pressing. The precompression tends to stick the plies togethersomewhat so that it is not only very difilcult to displace them fromtheir proper location, but also the assembly as a whole can be handledas a unit more quickly and easily. .Without precompression, the plieslie loosely one uponthe other and have to be handled with care to avoiddisplacement.

Besides useful applications in gluing porous sheet materials includingboth wood and paper,

the principles of my invention may also be applied in gluing togethermaterials of irregular shape, for example. in consolidating with anadhesive porous materials of a granular character, such as sawdust orground cork. After thoroughly mixing the granules with the adhesive. sothat a fair proportion of the surfaces carry a film of glue, apreliminary pressure may be applied to cause a proper transfer over themutually contacting surfaces along with penetration and the creation ofa residual film and then the pressure may be released so that the glueremaining on the surfaces becomes merely tacky rather than fiuid andthen the final consolidating pressure may be applied and a strong bondsecured as long as the final pressure is applied before the film of gluehas dried up so much as i tration and residual tacky film to be formed.

By this method, composite articles may be produced with exceptionalstrength and economy of glue.

The method of carrying out the present invention is not limited to anyparticular form of apparatus and it must be understood that theaccompanying drawings are simply diagrammatic representations ofsuitable machines for performing the various method steps.

In the drawings:

Figure 1 is a. diagrammatic side elevation of a suitable core plycoating apparatus.

Figure 2 is a diagrammatic plan view of the same.

Figure 3 is a diagrammatic side view of the preliminarily assembledplies, the plies being shown spaced apart and the thickness of theadhesive being considerably exaggerated.

Figure 4 is a similar diagrammatic view representing one manner ofperforming the preliminary compression step.

Figure 5 is a similar view representing an alternative method ofperforming the preliminary compression step.

Figure 6 is a diagrammatic representation of a final compression step.and

Figure '7 is a similar view of an alternative final compression step.

As shown in Figure 1, a core ply Ill may be passed between groovedrubber applicator rolls l I, I2, of substantially the characterdisclosed in my copending application Serial No. 191,096, now Patent2,188,456, where semi-fluid, relatively thick adhesive is applied. Theadhesive i preferably transferred to the rolls from receptacles l3, ll,by doctor rolls l5, l6.

Figure 2 is an exaggerated representation of an adhesive pattern,consisting of ribs ll of excess glue, alternating with spaces ll whichare' merely wetted with the adhesive. In practice, the adhesive ribs andthe intervening spaces will be relatively smaller than as represented inthe accompanying drawing, and any other desired adhesive pattern may besubstituted for that shown.

In Figure 3, upper and lower uncoated plies Is, 20 have been applied,and the preliminary compression step may be performed by pressure rolls2|, 22, as represented in Figure 4, or by a platen press, as shown inFigure 5, comprising a base 23, a head 24, toggle links 25, 26 andmeans, such as an air cylinder and piston 21, 28 .for applying force tothe toggle. The representation of the press and of the means foractuating the same is purely diagrammatic, as any suitable press may beemployed.

After a suflicient number of preliminarily compressed plywood panelshave been collected, two or three or more may be subjected to finalcompression in a hot press 30, or, alternatively, a greater number maybe subjected to a final cold pressing operation in a stack 3| in a coldpress comprising base 32 and head 33.

In carrying out the present method, when porous sheet materials, such aswood plies, are used, either a press, such as is shown at 23, 24, or apair of pressure rolls, such as 2 l, 22 may be used with desirableresults. With paper, roll pressure is preferred in most cases. Undersome conditions, it is desirable to cover the pressure rolls 2|, 22 withrubber, as indicated at 2|, 22', and, in such cases, the panels may beassembled on a conveyor and automatically carried through the bight ofthe rolls on their way to the final press. In other cases, the panelsmay be accumulated in small batches adjacent the glue spreader and thenpre-compressed in a platen press in small batches, instead of singly, asindicated in Figure 5. In some cases, the platen press is preferablebecause the application and release of pressure is somewhat more gradualand there is less tendency to displace or fracture the plies. The use ofrubber rolls for the same reason produces somewhat better results thanmetal surfaced rolls, due to the yielding action of the rubber.

Other modes of applying the principles of the invention may be employed,changes being made as regards the details described, providing thefeatures stated in any of the following claims or the equivalent ofsuch, be employed.

I claim:

1. The method of manufacturing plywood which comprises coating the upperand lower surfaces of core ply material with coatings of flowableadhesive, assembling with said core ply, upper and lower uncoated plieswith their surfaces in contact with the coated surfaces of the core ply,preliminarily compressing the assembled plies while the adhesive remainssoft and flowable under pressure, for only a momentary period of time,and substantially immediately releasing the compression, saidpreliminary compression being at a pressure sufficiently high to beeffective to cause transfer of the adhesive from the coated ply to theadjacent uncoated ply surfaces, to obtain appreciable and substantiallyuniform penetration of the plies by the adhesive, to squeeze a portionof the glue water into the wood and thereby leave on the surfaces aresidue of tacky adhesive sufilcient to avoid a starved joint, andsubsequently subjecting the assemblies thus produced to a final bondingcompression for a sumcient period of time to permanently set theadhesive and to permanently bond the plies together.

2. The method of manufacturing plywood which comprises coating the upperand lower surfaces of core ply material with coatings of relativelythick, semi-fluid adhesive in a pattern consisting of areas having an,excess of adhesive and substantially uncoated areas, assembling with thecoated core ply material, upper and lower uncoated plies with theirsurfaces in contact with the adhesive on the core ply material,preliminarily compressing the assembled plies while the adhesive remainssoft and flowable under 'pressure, for only a momentary period of time,and substantially immediately releasing said preliminary compression,said preliminary compression being at a pressure sufliciently high to beeffective to spread the adhesive from the excess areas to thesubstantially uncoated areas, to cause transfer of the adhesive from thecoated ply to the adjacent uncoated ply surfaces, to obtain appreciableand substantially uniform penetration of the plies by the adhesive, tosqueeze a portion .of the glue water into the wood and to leave on thesurfaces, a residue of tacky adhesive suflicient to avoid a starvedjoint, and subjecting the-assemblies thus produced to a finalcompression for a suflicient period of time to permanently set theadhesive and to permanently bond the plies together.

' HARRY G

